1. Field of the Invention
This invention relates to a novel transition metal which is useful as a catalyst for polymerization of olefins.
2. Prior Art
It is well known to produce ethylene polymers or ethylene-.alpha.-olefin copolymers with use of a catalyst composition comprising a zirconium compound, a transition metal compound such as titanocene and hafnocene compounds and an aluminoxane compound. This prior art catalyst is liable to form such a polymers which is of an extremely high catalytic activity and has a narrow molecular weight distribution and modal distribution. Such known transition metal compounds are represented by the formula (cyclopentadienyl).sub.2 MeRHal wherein R is a cyclopentadienyl or C.sub.1 -C.sub.6 alkyl group or halogen, particularly chlorine, Me is a transition metal, particularly zirconium and Hal is halogen, particularly chlorine. Specific examples are bis(cyclopentadienyl)zirconiumdichloride (Cp.sub.2 ZrCl.sub.2) and bis(cyclopentadienyl)zirconiummonomethylmonochloride Cp.sub.2 Zr(CH.sub.3)Cl as disclosed in Japanese Laid-Open Patent Publication No. 58-19309. U.S. Pat. No. 4,404,344 also discloses a zirconium compound represented by the formula Cp.sub.2 MeY.sub.2 wherein Me is zirconium, Y is hydrogen, a C.sub.1 -C.sub.5 alkyl group, a C.sub.1 -C.sub.5 metalalkyl group or a group of such as CH.sub.2 AlR.sub.2, CH.sub.2 CH.sub.2 AlR.sub.2 and CH.sub.2 CH(AlR.sub.2).sub.2 of which each R is a C.sub.1 -C.sub.5 alkyl group or a C.sub.1 -C.sub.5 metalloalkyl group.
Moreover, another compounds are well known from Japanese Patent Publication No. 7-37488 disclosing (C.sub.5 R'.sub.m).sub.p R".sub.s (C.sub.5 R'.sub.m)MeQ.sub.3-p and R".sub.s (C.sub.5 R'.sub.m).sub.2 MeQ' wherein Me is zirconium or hafnium, each (C.sub.5 R'.sub.m) is a cyclopentadienyl group or a substituted cyclopentadienyl group, R' each may be the same or different and are one member selected from the group consisting of hydrogen and C.sub.1 -C.sub.20 alkyl, alkenyl, aryl, alkylaryl and arylalkyl groups of which two adjacent members may form 4- through 6-membered condensed rings, R" is a C.sub.1 -C.sub.4 alkylene group, germanium, silicone, a phosphino group or an amino group which crosslink two rings (C.sub.5 R'.sub.m), Q each may be the same or different and are a C.sub.1 -C.sub.20 aryl, alkyl, alkenyl, alkylaryl or arylalkyl group or halogen, Q' is a C.sub.1 -C.sub.20 alkylidene, s=0 or 1, p=1 and, m=4 when s=1 and m=5 when s=0, and at least one of R' is a hydrocarbon group if m=5.
In recent years, there have been arising various demands for polyolefins in terms of physical properties and characteristics, such demands being directed to the production of polyolefins which are somewhat widened in molecular weight distribution or increased in molecular weight or which are completely free of halogen. It has been found that polyolefins tend to be effectively varied in properties and behaviors such as activity during polymerization depending on the type of a transition metal compound used therefor. Nowadays, a strong demand has been arising for a clean polyolefin free of halogen in view of problems in environment and hygienic.